So airlines allow 2 batteries of up to 160Wh (with airline approval) and as many 100Wh batteries as you can carry [note: I have not actually tried to show up to the TSA security line with a suitcase full of 100Wh batteries, so your mileage may vary].
A BiPAP machine uses 50-150 Watts, according to a random Google query, so you're looking at somewhere between 500 and 1400 Wh of total storage to get your 9 hours of sleep on a plane.
So what you're looking for is (a) a way to daisychain these batteries together so that you don't need to wake up ever 40 minutes to 2 hours to swap batteries and (b) a way to plug in your BiPAP machine, if your battery packs are all USB-C and your BiPAP isn't.